The present invention relates generally to air conditioning and refrigeration systems, and more specifically to a method of operating a cryogenic temperature control apparatus.
Conventional cryogenic temperature control systems typically store a compressed cryogen such as carbon dioxide, liquid nitrogen, etc. in a pressurized storage tank. The cryogen is directed along a conduit from the storage tank to an evaporator coil that extends through a heat exchanger. Relatively warm air is passed across the evaporator coil and is cooled by the evaporator coil. The cooled air is returned to a cargo compartment to pull down the temperature of the cargo compartment to a predetermined set point temperature. The warm air heats and vaporizes the cryogen in the evaporator coil. After the heat transfer has occurred, the vaporized cryogen is typically exhausted to the atmosphere.
Control systems that are used to operate existing cryogenic temperature control apparatuses are generally relatively complex, and regulate the temperature of the cargo to be at a set point temperature. These control systems require substantial computing power and programming skill to properly implement and operate. Additionally, the complexity of the existing control systems generally limits the flexibility of these temperature control apparatuses. The complexity and inflexibility of these control systems to adjust to various conditions of the cargo compartment can result in shutdown of the control apparatuses due to a relatively high consumption of fuel (e.g., carbon dioxide). This is especially problematic when the cryogenic temperature control apparatus is mounted to a vehicle for transportation between geographical locations.